I have contact a Addon Author, of a Addon that has not been updated in a long time. The Addon Author notated he wanted someone to take over, so what is acceptable period of time I should wait to here back from them?
If the author wrote in the comments or orum, that someone should take his addon to maintain it, and you did not hear anything from him/her, I guess it's not necessary to wait months.
I'd say 1 week is enough.
Which addon are you refering to?
Write a PM to Dolby or Cairenn in this forum, tell them the addon name + link, quote them/link them the text the addon dev wrote + the date and time (where he wanted someone else to help him/her) and tell them what time you contacted the author.